Compositions that are cured with heat or active lights such as UV rays are used in a wide range of fields including coating materials, UV or heat curable paints, molding materials, adhesives, inks, resist materials, optical materials, stereolithography materials, printing plate materials, dental materials, polymer battery materials and polymer materials. For example, uses as optical materials include coating materials for optical lenses or films, cladding materials for optical fibers, and optical adhesives for optical fibers or optical lenses.
Curable compositions are mainly composed of a photopolymerization or thermal polymerization initiator, a compound with an ethylenically unsaturated double bond that is cured by polymerization reaction, and additives. Types of the compositions are wide-ranged depending on use. In particular, the curing technique by the application of active energy rays such as UV rays and electron beams enables room temperature curing and quick drying without solvents, and is attractive in terms of environmental issues, energy saving, operation safety and production costs. Demands for this curing technique have been increasing.
In the development of color filters in particular, pigment-dispersed resists for color filters that are cured with light have been studied actively for the purposes of increased productivity and finer patterning. Studies have been also carried out to increase the plate-making speed and fineness in color proofs and printing plates. Additionally, solder resists for printed boards have been studied.
Compounds for curable compositions are selected depending on what wavelength of light they are sensitive to or how they are polymerizable. Compounds with an ethylenically unsaturated double bond and additives are selected depending on polymerizability and desired properties of cured products, and are used in combination as curable compositions. Demands for curable compositions in the above fields have been increasing, and there has been a demand for compositions that are curable with lower energy, compositions that are cured more quickly, compositions capable of forming finer patterns, compositions that are curable to a greater depth, compositions with higher storage properties, and compositions having enhanced developability.
However, some of the compounds with an ethylenically unsaturated double bond and additives have encountered problems that (1) sufficient energy to induce photopolymerization cannot be obtained, (2) storage properties are bad, (3) the light cannot reach deep in the composition because of the desired thickness of cured product, resulting in insufficient curing, (4) the curable composition is damaged by oxygen during contact with air, and (5) good developability is not obtained. These problems are dealt with by applying greater light energy, using an excessive amount of a photopolymerization initiator, or providing an oxygen-shielding membrane. However, curable compositions of excellent photocuring properties or storage properties are desired for energy saving and reduction of production costs.
In response to such demands, curable compositions having a thiol compound are increasingly studied recently. For example, JP-A-H10-253815 (Patent Document 1) discloses photopolymerizable compounds that contain a polyfunctional thiol and an initiator selected from biimidazole compounds, titanocene compounds, triazine compounds and oxazole compounds. JP-A-2000-249822 (Patent Document 2) discloses a photopolymerization initiator comprising a sensitizer, an organoboron complex and a mercapto compound. However, such attempts to increase the sensitivity with polyfunctional thiols result in bad storage properties.
JP-A-2004-149755 (Patent Document 3) teaches that secondary or tertiary thiol compounds give curable compositions having excellent photocurability and storage stability. However, the increase of aliphatic groups may likely deteriorate developability.    Patent Document 1: JP-A-H10-253815    Patent Document 2: JP-A-2000-249822    Patent Document 3: JP-A-2004-149755